/*
 * Copyright (C) 2018 The Guava Authors
 *
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
 * in compliance with the License. You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software distributed under the License
 * is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
 * or implied. See the License for the specific language governing permissions and limitations under
 * the License.
 */

package com.google.common.collect;

import static com.google.common.base.Preconditions.checkNotNull;

import com.google.common.annotations.GwtCompatible;
import com.google.common.primitives.Ints;

import java.util.Collection;
import java.util.Map;
import javax.annotation.CheckForNull;

/**
 * An implementation of ImmutableMultiset backed by a JDK Map and a list of entries. Used to protect
 * against hash flooding attacks.
 *
 * @author Louis Wasserman
 */
@GwtCompatible
@ElementTypesAreNonnullByDefault
final class JdkBackedImmutableMultiset<E> extends ImmutableMultiset<E>
{
    private final Map<E, Integer> delegateMap;
    private final ImmutableList<Entry<E>> entries;
    private final long size;

    static <E> ImmutableMultiset<E> create(Collection<? extends Entry<? extends E>> entries)
    {
        @SuppressWarnings("unchecked")
        Entry<E>[] entriesArray = entries.toArray(new Entry[0]);
        Map<E, Integer> delegateMap = Maps.newHashMapWithExpectedSize(entriesArray.length);
        long size = 0;
        for (int i = 0; i < entriesArray.length; i++)
        {
            Entry<E> entry = entriesArray[i];
            int count = entry.getCount();
            size += count;
            E element = checkNotNull(entry.getElement());
            delegateMap.put(element, count);
            if (!(entry instanceof Multisets.ImmutableEntry))
            {
                entriesArray[i] = Multisets.immutableEntry(element, count);
            }
        }
        return new JdkBackedImmutableMultiset<>(
                delegateMap, ImmutableList.asImmutableList(entriesArray), size);
    }

    private JdkBackedImmutableMultiset(
            Map<E, Integer> delegateMap, ImmutableList<Entry<E>> entries, long size)
    {
        this.delegateMap = delegateMap;
        this.entries = entries;
        this.size = size;
    }

    @Override
    public int count(@CheckForNull Object element)
    {
        return delegateMap.getOrDefault(element, 0);
    }

    @CheckForNull
    private transient ImmutableSet<E> elementSet;

    @Override
    public ImmutableSet<E> elementSet()
    {
        ImmutableSet<E> result = elementSet;
        return (result == null) ? elementSet = new ElementSet<>(entries, this) : result;
    }

    @Override
    Entry<E> getEntry(int index)
    {
        return entries.get(index);
    }

    @Override
    boolean isPartialView()
    {
        return false;
    }

    @Override
    public int size()
    {
        return Ints.saturatedCast(size);
    }
}
